1. Field of the Invention
This invention relates generally to apparatus and methods for manufacturing optical and photonic devices for fiber optical signal transmission systems. More particularly, this invention is related to configuration and method of manufacturing multiple channel optical and photonic attenuator for use in wide-band optical communication sub-system or system.
2. Description of the Related Art
Recent development of the mechanical anti-reflection switch for implementation as optical modulators is still faced with a technical limitation. The configuration is mostly employed as a single channel device and alignment for more than one channel would be costly wherever multi-channel applications are required for state-of-the-art optical network communication system. The mechanical anti-reflection switch configuration, as will be further described below, be conveniently manufactured by a low-cost silicon-based micro electromechanical systems (MEMS) technique to fulfill the objectives of providing an optical modulator with high production volume and low cost. In a preferred form, this device has a multiple-layer film stack of polysilicon/silicon nitride/polysilicon. The polysilicon layer is doped to function as an electrode layer. A precisely controlled air gap between the film stack and the substrate allows a controllable switching operation of turning the modulator from a reflecting state to an anti-reflecting state. The multi-layer film configuration is controllable with low drive voltage, large optically active area, and excellent performance characteristics over a broad spectral range. The modulator also performs well in many system applications. However, as state-of-the-art wide-band optical communication system now requires a multi-channel buffered subsystem to properly attenuate and redistribute the optical signals, a conventional single channel device cannot satisfy the system requirements to carry out the multiple channel fast attenuation process.
Based on the principle of the well-known Fabry-Perot interferometer constructed by Charles Fabry and Alfred Perot in 1897, Goossen discloses in U.S. Pat. Nos. 5,943,155 and 5,949,571, entitled xe2x80x9cMARS Optical Modulatorsxe2x80x9d, a double polysilicon MARS (mechanical antireflection switch) device where the shorting between the lower polysilicon metalization and the silicon substrate is prevented by providing an insulating layer on the surface of the silicon substrate. Goossen teaches a modulator configuration using the reflection modulation of the Fabry-Perot interferometer with improved reliability. The disclosures of these two patents are hereby incorporated as reference in this Application. The configuration disclosed by Goossen as shown in FIG. 1 however is still limited to handle single channel of optical transmissions. For an optical signal transmission system that handles signals distributions between multiple interconnected networks with multiple optical fibers, the configuration of Goossen""s disclosures are still insufficient to resolve the limitations encountered by those of ordinary skill in the art.
Therefore, a still need exists in the art in the field of the optical signal transmission systems to provide a configuration and method of manufacture to provide multiple channel attenuator such that the limitations encountered by current single configuration can be overcome. It is further desirable that the multiple channel attenuators would allow for different attenuation characteristics controllable for each individual channel such that signal transmission in each channel can be flexibly adjusted. This principle is similar to the transmission mode of a Fabry-Perot interferometer. The designed air gap modulation shall meet the requirement. For a specific wavelength, xcex, the gap length shall equal to mxcex/4 (when m is even the mode shall be anti-reflection, m is odd the mode shall be reflection. In addition, the desirable multi-channel configuration also provides a benefit to significantly reduce the production cost because the channel to channel alignment processes as that required in the conventional optical devices are no longer necessary.
It is therefore an object of the present invention to provide new and improved configuration and methods for manufacturing multi-channel optical and/or photonic attenuators with each attenuator flexibly controlled by separate control circuits such that flexible multi-channel optical signal transmission can be conveniently carried out. With the new and improved structural and control configurations, the limitations and difficulties of the prior art can be resolved. The present invention also requires only one alignment for all channels and hence significantly reduces the cost in package process. Further, the present invention allows the manufacture of flexibly adjustable number of channels on a single silicon wafer at one time, i.e. a lower number of channels can be diced out from the dies with a higher number of channels.
Another object of the present invention is to provide the multi-channel optical attenuators by using the micro-electromechanical system (MEMS) process. The attenuators are integrated on the silicon wafer substrate providing desired multi-channel attenuation with optimized insertion loss for the optical signals in the optical communication system or sub-system.
Another object of the present invention is to provide an array of multi-channel optical attenuating devices by using the micro-electromechanical system (MEMS) process to form the optical attenuator devices, each with cross-shaped chamber. An optical active area is formed at the center of the cross-shaped chamber to provide high sensitivity adjustment.
Briefly, in a preferred embodiment, this invention discloses an array of multi-channel optical attenuating devices. This array of multi-channel attenuating devices includes a plurality of electro-optical devices support on a conductive substrate. Each of these electro-optical devices includes a membrane having an optically transparent portion. Each of these electro-optical devices further includes a flexible support for positioning the optically transparent portion of the membrane spaced from the substrate for defining an air gap. The air gap constitutes a cross-shaped gap-chamber having a horizontally and vertically elongated chambers extended from a central intersection area. The central intersection area constitutes an optical active area. Each of these electro-optical devices further includes a means for applying an electrical bias between the conductive substrate and the membrane to adjust and control an air-gap thickness at the optical active area between the conductive substrate and the membrane. Each channel in the array can be individually adjusted to accommodate the requirement for the optical network system. For the array of channels, fiber alignment can only apply to any one of the channels in the array and hence the cost of package is significantly reduced.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.